The present invention relates to a device for protecting a high-pressure gas tank of a motor vehicle. High-pressure gas tanks, which are generally also referred to as composite tanks, composite-material tanks, or fiber-composite tanks, typically have fully or partially fiber-reinforced material layers which surround a liner. The liner is often formed from aluminum or steel and accommodates the compressed gases such as, for example, compressed air, oxygen, methane, hydrogen, carbon dioxide, etc. Plastics liners (full-composite tanks) are also known. Such high-pressure gas tanks are employed, for example, in vehicles which are operated with compressed natural gas, often referred to as CNG, or with hydrogen.
When such high-pressure gas tanks are employed there is the risk of the structure of the latter being weakened by the effect of heat. The use of safety valves, so-called thermal pressure release devices (TPRD) is known from the prior art. These safety valves serve as fire protection. The design embodiment of the safety valves or of the fire-protection valves, respectively, is predefined by the standard EC79/2009, for example. In the case of a direct effect of heat (for example by flames) on these safety valves the gas which is stored in the high-pressure gas tank is released to the environment. The safety valves release the gas as soon as a minimum temperature at the safety valve is exceeded. The valves are typically disposed so as to be mutually spaced apart by approx. 1 m along the longitudinal direction of the high-pressure gas tank. The few valves along the large pressure vessels herein may only take into consideration a catchment area which is very limited in spatial terms. A small localized flame which acts on the tank between two valves may thus heavily damage the high-pressure gas tank without the safety installation being activated. The damage to the high-pressure gas tank, or the damage to the load-bearing fiber-composite material, respectively, which is created by the effect of heat of a localized flame may lead to the high-pressure gas tank failing and, in an extreme case, bursting. The high-pressure gas tanks store gases at a pressure of up to 875 bar. Accordingly, bursting of the high-pressure gas tank may lead to very dangerous damage to the entire vehicle. The fiber-composite layers typically bear the major part of the stress. The damage to the fiber-reinforced material layer by thermal or mechanical influences may thus rapidly lead to a significant reduction in the durability, or to a significant weakening, respectively, of the component.
A device in which a layer having a hydrate is disposed above or below a high-pressure gas tank is known from US 2011/0079403 A1. According to US 2011/0079403 A1, these layers are fastened on a panel, so as to be spaced apart from the high-pressure tank. The safety valves and the supply line thereto are disposed between the panel and the high-pressure gas tank. In order for the safety valves and the lines thereof to be fastened, loops around the high-pressure gas tank are provided. The assembly of these safety valves and of the supply line thereto is complex. Furthermore, this embodiment occupies a comparatively large installation space. According to this publication, the tank is protected in that the heat is absorbed in a localized manner by an increase in the volume of the layer containing the hydrate.
It is a preferred object of the technology disclosed herein to reduce or eliminate the disadvantages of the previously known high-pressure gas tanks.
This and other objects are achieved by a device for protecting a high-pressure gas tank of a motor vehicle, for example of a vehicle which may be charged with natural gas or hydrogen. The device has an intumescent layer which at least partially shields the high-pressure gas tank from a source of fire. The intumescent layer furthermore has an intumescent metal material.
Shielding in this context means that the intumescent layer at least partially reduces and/or delays mechanical or thermal influences. In other words, the intumescent layer has the effect that the high-pressure gas tank in that region of the high-pressure gas tank that is shielded by the intumescent layer is not heated as rapidly and/or does not absorb shocks as strongly as in those regions in which the intumescent layer does not shield the high-pressure gas tank. In particular, the thermal shielding effect is such that an effective fire protection, which at least appreciably delays the effect of the fire, is created.
The term intumescent refers generally to the expansion or the swelling, that is to say the increase in size, of a solid body under the influence of temperature. In terms of fire protection, the term refers to the swelling or foaming, respectively, of materials. Intumescent materials thus increase in volume and decrease in density under the effect of heat. Herein, the volume increases significantly, often by a multiple, beyond the usual amount of thermal expansion. The physical properties are significantly modified. For example, an insulation layer is created by the swelling or foaming, respectively.
In the technology disclosed herein, the intumescent layer functions as a heat brake and as mechanical protection. As opposed to metallic foams, hydrates can offer a mechanical protection only to a very minor extent. Moreover, intumescent metal materials, such as intumescent metallic foams, have the advantage that in the non-foamed original state the intumescent metal materials have a thermal conductivity which is comparatively high as opposed to other intumescent materials. If intense heating now arises in a localized manner at any point, for example by a localized flame, this heat is distributed across a comparatively large area of the intumescent metal layer. A more homogenous heating of the intumescent metal material results. The distribution of the locally acting heat across the area initially reduces the speed at which that point on which the heat acts in a localized manner is heated. Furthermore, a metallic foam which then protects the tank across a large area from the local effect of heat may already be built up over a large area even in the case of a small localized effect of heat by a small flame. A further advantage of the comparatively high thermal conductivity in the initial state prior to the increase in volume is to be seen in that the heat effect which is created in a localized manner may be transmitted onward rapidly or more rapidly, respectively, to the nearest safety valve. The safety valve may thus open and release the stored gas more rapidly or earlier, respectively, as compared to the prior art. Moreover, the intumescent metal material may protect the fiber-reinforced material layers from mechanical influences.
The intumescent layer may be fastenable directly to the high-pressure gas tank. For example, the intumescent layer may be adhesively bonded to the high-pressure gas tank, or may be held directly, preferably bear, on the high-pressure gas tank by other fastening measures. In one further design embodiment, the intumescent layer is spaced apart from the outermost layer of the high-pressure gas tank by a minor spacing, for example by less than 5 cm, preferably less than 1 cm. By way of such a design embodiment, the installation space for the high-pressure gas tank in the motor vehicle may be further reduced, for example by 10 to 50 mm. The gap between the intumescent layer and the outermost layer of the high-pressure gas tank represents an additional insulation layer. In particular, the high-pressure gas tank is thus preferably designed in such a manner that the safety valves are not shielded from the flame by the intumescent layer. The responsive behavior of the safety valves may thus advantageously be further improved.
The intumescent metal material preferably has a metal powder and a metal hydride, for example titanium hydride. Furthermore, the intumescent metal material is preferably designed as an intumescent aluminum material. The intumescent aluminum material preferably comprises an aluminum alloy and a propellant. For example, the intumescent layer may be embodied as an aluminum alloy having a titanium hydride propellant. Such aluminum foams under the effect of heat expand by a factor of 4, for example, wherein a foam having a porous structure is created. In the foamed state, the aluminum foams have a density of approx. 0.6 g/cm3, for example. As compared with other intumescent metal materials, the intumescent aluminum material in the non-foamed original state has a lower density. Other metal hydrides may also be used as a propellant. Furthermore, copper, zinc, lead, or steel/iron may also be employed besides aluminum, for example.
The intumescent layer may be embodied as a metal sheet, as a plate, or as a foil. For example, the intumescent layer may at least be partially wrapped as a foil around the high-pressure gas tank. Alternatively and/or additionally, a semi-finished product may be fitted to the tank. Furthermore, the intumescent layer may be configured as a profile of an arcuate cross section, in particular as a C-shaped, or U-shaped, or V-shaped profile, and/or as a tube. The C-shaped design embodiment of the intumescent layer 20 as compared to the intumescent layer which is of a tubular cross section gives rise to the advantage that the weight may be reduced without greatly restricting the protection of the high-pressure gas tank.
Preferably, the high-pressure gas tank is at least partially received in the interior of the intumescent layer. Such a design embodiment is particularly cost-effective in production and has advantageous structural dimensions. The profile which is arcuate in the cross section may enclose at least half, preferably at least 75% of the circumference of the high-pressure gas tank.
The intumescent layer advantageously has a wall thickness of 0.1 mm to 40 mm, preferably of 3 mm to 20 mm, and particularly preferably of 6 mm to 15 mm. Such a design embodiment of the intumescent layer has a favorable ratio of weight to shielding effect, both in mechanical as well as thermal terms.
Advantageously, the intumescent layer expands by at least 1.5 times, preferably by at least 2 times, and particularly preferably by at least 4 times the original wall thickness thereof.
At least one fastener for fastening a safety valve in or to the intumescent layer, respectively, may preferably be provided. For example, the intumescent layer, preferably along the longitudinal axis, may have integrally configured form-fitting structures, for example clamps, bores, threads, and/or inserts, to which the safety valve or safety valves, respectively, are fastenable. By way of this advantageous design embodiment it may be possible to replace the previously employed buckles and, therefore, to achieve fastening of the safety valves, or of the lines leading to the safety valves, respectively, in a cost-effective manner. By direct contact with the intumescent layer, the heat may be transferred by conduction to the safety valve, on account of which the responsive behavior of the safety valve or of the safety valves, respectively, may additionally be improved. The safety valve is preferably disposed on the external side of the intumescent layer. In other words, the liner of the high-pressure gas tank is disposed on the one side of the intumescent layer, and the safety valve is disposed on the other side.
The technology disclosed herein likewise includes a high-pressure gas tank equipped with the device described herein for protecting the high-pressure gas tank.
The high-pressure gas tank preferably has a fiber-reinforced layer. The fiber-reinforced layer may enclose a liner, for example from aluminum, of the tank. CFRP and GFRP are employed as fiber-reinforced plastics. The intumescent layer is advantageously at least partially applied to the external surface of the fiber-reinforced layer.
The technology disclosed herein preferably includes a method for producing the high-pressure tank disclosed herein. The method preferably includes the following acts:                providing a core of a high-pressure gas tank;        providing the intumescent layer; and        at least partially sliding the intumescent layer onto the core, or at least partially wrapping the core with the intumescent layer.        
A core of the high-pressure gas tank may preferably be interference fit into the interior of the arcuate profile. Furthermore, the method may advantageously include the act of fastening at least one safety valve to the external surface of the intumescent layer. Here, the core is considered to be the liner of the high-pressure gas tank including any potential additional material layers, for example a fiber-reinforced material layer.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.